Vacuum suction machines have come into widespread use for the removal of hazardous materials. Such machines typically employ a number of filter stages. The initial filters are used to remove debris and particles of larger size, and a final stage usually consists of a special filter known in the art as a high efficiency particulate air or HEPA filter. HEPA filters are especially designed to remove particles from air passing through the filter where the particle size extends down to microscopic levels.
HEPA filters, like other filters, become clogged with use and have to be replaced periodically. It is important that a replacement HEPA filter have the same capacity and specifications as the original HEPA filter because when a HEPA filter is replaced, it is enclosed within the machine and cannot ordinarily be seen by the operator. And an operator may not always take the precaution of opening the machine to make sure that the HEPA filter being used is a proper one.
It is also possible that some operators who are particularly careless may remove the HEPA filter and use the vacuum suction machine for other, more conventional uses. When the operator replaces the machine after conventional use, a careless operator may fail to put the HEPA filter back in the machine or to note on the machine that it is not equipped with a HEPA filter. Subsequent operation of such a machine without a HEPA filter for removal of hazardous material would obviously present a hazard to a subsequent operator.
It is also important that HEPA filters be designed for proper sealing with the housing for the vacuum motor because there is a substantial pressure drop across the filter and if there is any leakage of contaminated air around, rather than through the filter, such a condition could also present a hazard to the environment and to operators.